Trench schottky rectifier device and method for manufacturing the same

ABSTRACT

A method for fabricating a trench Schottky rectifier device is provided. At first, a plurality of trenched are formed in a substrate of a first conductivity type. An insulating layer is formed on sidewalls of the trenches. Then, an ion implantation procedure is performed through the trenches to form a plurality of doped regions of a second conductivity type under the trenches. Subsequently, the trenches are filled with conductive structure such as metal structure or tungsten structure. At last, an electrode overlying the conductive structure and the substrate is formed. Thus, a Schottky contact appears between the electrode and the substrate. Each doped region and the substrate will form a PN junction to pinch off current flowing toward the Schottky contact to suppress the current leakage in a reverse bias mode.

This is a divisional application of co-pending, U.S. application Ser.No. 15/360,155, filed Nov. 23, 2016, which is a divisional of U.S. Pat.No. 9,536,976, filed Nov. 13, 2015, which is a divisional of U.S. Pat.No. 9,219,170, filed Oct. 29, 2014, which is a divisional of U.S. Pat.No. 8,890,279, filed Nov. 15, 2013, which is a divisional of U.S. Pat.No. 8,618,626, filed Oct. 12, 2010, the subject matter of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a trench Schottky rectifier device andrelated manufacturing method, and more particularly to a trench Schottkyrectifier device with embedded doped regions.

BACKGROUND OF THE INVENTION

A Schottky diode is a unipolar device using electrons as carriers, whichis characterized by high switching speed and low forward voltage drop.However, the Schottky diodes have limitation of relatively high reverseleakage current. The characteristics of the Schottky barrier aredetermined by the metal work function of the metal electrode, the bandgap of the intrinsic semiconductor, the type and concentration ofdopants in the semiconductor layer, and other factors. In contrast tothe Schottky diode, a PN junction diode is a bipolar device that canpass more current than the Schottky diode. However, the PN junctiondiode has a forward voltage drop higher than that of the Schottky diode,and takes longer reverse recovery time due to a slow and randomrecombination of electrons and holes during the recovery period.

A Schottky rectifier device has been described in U.S. Pat. No.6,710,418 to overcome the current leakage problem. Please refer to FIG.1, a schematic diagram illustrating the Schottky rectifier device withinsulation-filled trenches. The Schottky rectifier device 100 includes aheavily-doped N-type substrate 102, a lightly-doped N-type epitaxiallayer 104 overlying the substrate 102, and a plurality ofinsulation-filled trenches 114 extending from the top surface of theepitaxial layer 104. There are two P-type silicon strips 108 onsidewalls of each trench 114. An anode electrode 110 is provided on thetop surface of the epitaxial layer 104 and a cathode electrode 116 isprovided on the bottom surface of the substrate 102. The anode electrode110 forms a Schottky contact with the underlying epitaxial layer 104,and is in contact with the P-type silicon strips 108.

In the Schottky rectifier device 100, the Schottky contact between theanode electrode 110 and the epitaxial layer 104 results in low forwardvoltage drop. Furthermore, the P-type strips 108 can prevent the lowaccumulation threshold to reduce the current leakage problem of theSchottky rectifier device 100. However, the P-type strips 108 occupysome areas of the Schottky contact, and thus the size of the Schottkyrectifier device 100 should be enlarged to keep the equivalent area ofthe Schottky contact to prevent increasing the forward voltage drop andconsuming more power. Therefore, an improved Schottky rectifier devicewith low current leakage but without increasing the size thereof isdesired. There is a need of providing the improved Schottky rectifierdevice in order to obviate the drawbacks encountered from the prior art.

SUMMARY OF THE INVENTION

The present invention provides a trench Schottky rectifier device havinglow forward voltage drop and low reverse leakage current.

The present invention also provides a method for manufacturing a trenchSchottky rectifier device having low forward voltage drop and lowreverse leakage current.

In accordance with an aspect of the present invention, the trenchSchottky rectifier device includes a substrate of a first conductivitytype; a plurality of trenches formed in the substrate; and an insulatinglayer formed on sidewalls of the trenches. The trenches are filled withconductive structure. An electrode overlies the conductive structure andthe substrate to form a Schottky contact between the electrode and thesubstrate. There are a plurality of doped regions of a secondconductivity type formed in the substrate and located under thetrenches. Each doped region and the substrate will form a PN junction topinch off current flowing toward the Schottky contact in a reverse biasmode.

In accordance with another aspect of the present invention, a method forfabricating a trench Schottky rectifier device is provided. At first, aplurality of trenched are formed in a substrate of a first conductivitytype. An insulating layer is formed on sidewalls of the trenches. Then,an ion implantation procedure is performed through the trenches to forma plurality of doped regions of a second conductivity type under thetrenches. Subsequently, the trenches are filled with conductivestructure such as poly-silicon structure or tungsten structure. At last,an electrode overlying the conductive structure and the substrate isformed. Thus, a Schottky contact appears between the electrode and thesubstrate. Each doped region and the substrate will form a PN junctionto pinch off current flowing toward the Schottky contact to suppress thecurrent leakage in a reverse bias mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore readily apparent to those ordinarily skilled in the art afterreviewing the following detailed description and accompanying drawings,in which:

FIG. 1 (prior art) is a cross-sectional view schematically illustratingthe conventional Schottky rectifier device;

FIG. 2 is a cross-sectional view illustrating a preferred embodiment ofa trench Schottky rectifier device according to the present invention;

FIGS. 3A-3H schematically illustrate the manufacturing method forforming the trench Schottky rectifier device of FIG. 2;

FIG. 4 is a cross-sectional view illustrating another preferredembodiment of a trench Schottky rectifier device according to thepresent invention;

FIGS. 5A-5G schematically illustrate the manufacturing method forforming the trench Schottky rectifier device of FIG. 4;

FIG. 6 is a cross-sectional view illustrating a further preferredembodiment of a trench Schottky rectifier device according to thepresent invention; and

FIGS. 7A-7J schematically illustrate the manufacturing method forforming the trench Schottky rectifier device of FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more specifically withreference to the following embodiments. It is to be understood thatother embodiment may be utilized and structural changes may be madewithout departing from the scope of the present invention. Also, it isto be understood that the phraseology and terminology used herein arefor the purpose of description and should not be regarded as limiting.The use of “including,” “comprising,” or “having” and variations thereofherein is meant to encompass the items listed thereafter and equivalentsthereof as well as additional items. Unless limited otherwise, the terms“connected,” “coupled,” and “mounted,” and variations thereof herein areused broadly and encompass direct and indirect connections, couplings,and mountings.

Please to FIG. 2, a cross-sectional view illustrating a preferredembodiment of a trench Schottky rectifier device according to thepresent invention. Please note that the article “a” or “an” may be usedfor some elements, but the number of the elements is not limited to“one”. The amount may vary with different applications. As shown in FIG.2, the trench Schottky rectifier device 2 includes a substrate 20, aplurality of trenches 21, doped regions 22, polysilicon structure 23,oxide layers 210, 213, 24, an adhesion layer and an electrode 26. Thesubstrate 20 includes a heavily-doped N-type silicon layer 201 and alightly-doped N-type epitaxial layer 202. The plurality of trenches 21are formed in the epitaxial layer 202 and extending from the top surfaceof the epitaxial layer 202. The sidewalls of the trenches 21 are coveredwith the oxide layers 213 and the trenches 21 are filled with thepolysilicon structure 23 which protrudes from the top surface of theepitaxial layer 202. The doped regions 22 of P-type conductivity areformed in the epitaxial layer 202 and located under the trenches 21, andin contact with the polysilicon structure 23 at bottoms of the trenches21.

An isolation layer including the oxide layers 210 and 24 is provided tocover a portion of the epitaxial layer 202 at an inactive area of thetrench Schottky rectifier device 2 and separate the trench Schottkyrectifier device 2 from other devices. The electrode 26 is provided onthe oxide layer 24, the exposed epitaxial layer 202, and the protrudingpolysilicon structure 23. The electrode 26 is made of metal material,for example Al, Al alloy or other suitable metal material. An adhesionlayer 25 made of Ti or TiN may be provided between the electrode 26 andthe substrate 20 to enhance the bonding of the electrode 26 to thesubstrate 20. According to the described structure, Schottky contactsare formed on the interface between the metal electrode 26 (or theadhesion layer 25) and the epitaxial layer 202.

In a forward bias mode, the Schottky contacts between the metal layer 25and the epitaxial layer 202 bring low forward voltage drop and consumeless power. Furthermore, the P-type doped regions 22 and thelightly-doped N-type epitaxial layer 202 form PN junctions. In a reversebias mode, depletion regions of the PN junctions are widened and thecarrier density therein is very small. Hence, the widened depletionregions of neighboring PN junctions will hinder and pinch off thecurrent flow under the Schottky contacts. Based on the pinch-off effect,the reverse current leakage is thus suppressed. It is to be noted thatthe P-type doped regions 22 are located under the trenches 21 and do notoccupy the area of the Schottky contacts. Hence, it is not necessary toenlarge the size of the trench Schottky rectifier device 2 to compensatefor the reduced area of the Schottky contacts.

FIGS. 3A-3H illustrate a manufacturing method for forming the trenchSchottky rectifier device of FIG. 2 according to the present invention.As shown in FIG. 3A, a stack structure including a substrate 20, a maskoxide layer 210 and a first patterned photoresist layer 211 with atrench pattern is provided. The substrate 20 includes a heavily-dopedN-type silicon layer 201 and a lightly-doped N-type epitaxial layer 202.The mask oxide layer 210 on the substrate 20 is grown by thermaloxidation or deposition. The mask oxide layer 210 is then subjected toan etching step to partially remove the mask oxide layer 210 to expose aportion of the lightly-doped N-type epitaxial layer 202 according to thetrench pattern.

In FIG. 3B, the first patterned photoresist layer 211 is stripped off.Then, the epitaxial layer 202 is etched through openings of the maskoxide layer 210 to form the trenches 21 in the epitaxial layer 202. AnO₂ based thermal procedure is performed to form a thin sacrificial oxidelayers 212 on sidewalls and bottoms of the trenches 21. P-type dopantssuch as B ions or BF₂ are then implanted into the epitaxial layer 202through the bottoms of the trenches 21 to form the doped regions 22under the trenches 21. The doped regions 22 play an important role insuppressing the leakage current as described above.

In FIG. 3C, the thin sacrificial oxide layer 212 has been removed andgate oxide layers (insulating layers) 213 are formed to cover thesidewalls and the bottoms of the trenches 21. It is to be noted thatafter removing the thin sacrificial oxide layers 212, the smoothness ofthe surfaces of the trenches 21 are improved. The oxide layers 213 onthe bottoms of the trenches 21 are further etched off to expose thedoped regions 22.

FIG. 3D shows that the trenches 21 are filled with a polysiliconstructure 23. In an embodiment, a polysilicon layer is first grown tocover the structure of FIG. 3C by a chemical vapor deposition (CVD)procedure, and then the polysilicon layer is subjected to an etch-backprocedure to remove a portion of the polysilicon layer out of thetrenches 21. It is to be noted that the polysilicon structure 23 may bea polysilicon layer with or without dopants. If an ion implantationprocedure is performed after the formation of the polysilicon layer tointroduce dopants such as B ions into the polysilicon layer, a thermaldrive-in step or an annealing step is optionally performed to allowbetter diffusion of the dopants or activate the dopants.

In FIG. 3E, an oxide layer 24 and a second patterned photoresist layer214 defining the device area of the trench Schottky rectifier device 2are sequentially formed on the structure of FIG. 3D. The oxide layer 24,for example, is formed from tetraethyl orthosilicate (TEOS) by a lowpressure CVD (LPCVD) procedure with high deposition rate. Then, theoxide layers 24 and 210 are partially etched according to the secondpatterned photoresist layer 214 to expose portions of the top surface ofthe epitaxial layer 202 and the polysilicon structure 23. FIG. 3F showsthe obtained structure in which the second patterned photoresist layer214 has been stripped off, the resultant structure is obtained as shownin FIG. 3F. The combination of the oxide layers 210 and 24 may beconsidered as an isolation layer covering the inactive area of thetrench Schottky rectifier device 2 to separate the trench Schottkyrectifier device 2 from other devices.

At last, the electrode 26 is formed on the obtained structure. Theadhesion layer 25 may be formed prior to the formation of the electrode26 to enhance the bonding of the electrode 26 to the substrate 20. Theelectrode 26 and the adhesion layer 25 may be formed, but not limitedto, as follows. At first, a metal sputtering procedure is performed onthe structure of FIG. 3G to form the adhesion layer 25. Therefore, thewhole wafer is blanketed by the adhesion layer 25. In an embodiment, theadhesion layer 25 is made of Ti or TiN. Subsequently, another metalsputtering procedure is performed on the adhesion layer 25 to form theelectrode metal layer 26 overlying the adhesion layer 25. In anembodiment, the electrode metal layer 26 is made of Al or Al alloy. Arapid thermal processing (RTP) procedure may be performed after theelectrode metal layer 26 is formed, so as to correct the defectsresulting from the metal sputtering procedure. Then, a third patternedphotoresist layer 216 is formed over the electrode metal layer 26.Portions of the electrode metal layer and the adhesion layer 25 areetched off to form the electrode 26 according to the third patternedphotoresist layer 216. After the third patterned photoresist layer 216is stripped off, a sintering process may be performed to enhanceadhesion of the metal layer 25 to the substrate 20, the polysiliconstructure 23 and the oxide layer 24. It is to be noted that thesintering procedure may be performed after each metal sputteringprocess. The resultant structure of the trench Schottky rectifier device2 has been described with reference to FIG. 2. Although there aretrenches 21 and doped regions 22 in the inactive area of the trenchSchottky rectifier device 2 of FIG. 2, they are not essential componentsaccording to the present invention.

FIG. 4 is a cross-sectional view illustrating another preferredembodiment of a trench Schottky rectifier device according to thepresent invention. The trench Schottky rectifier device 3 includes asubstrate 30, a plurality of trenches 31, doped regions 32, metalstructure 35, oxide layers 310, 313, an adhesion layer 34 and anelectrode 36. The substrate 30 includes a heavily-doped N-type siliconlayer 301 and a lightly-doped N-type epitaxial layer 302. The pluralityof trenches 31 are formed in the epitaxial layer 302 and extending fromthe top surface of the epitaxial layer 302. The sidewalls of thetrenches 31 are covered with the oxide layers 313 and the trenches 31are filled with the metal structure 35. The metal structure 35 may bemade of W or other suitable metal. The doped regions 32 of P-typeconductivity are formed in the epitaxial layer 302 and located under thetrenches 31. The bottoms of the metal structure 35 are in contact withthe doped regions 32.

The oxide layer 310 is provided to cover an inactive area of the trenchSchottky rectifier device 3 and separate the trench Schottky rectifierdevice 3 from other devices. An electrode 36 is provided on the oxidelayer 310, the exposed epitaxial layer 302, and the metal structure 35.The electrode 36 is made of metal material, for example Al, Al alloy orother suitable metal material. An adhesion layer 34 made of Ti or TiNmay be provided between the electrode 36 and the substrate 30 to enhancethe bonding of the electrode 36 to the substrate 30. In particular, theadhesion layer 34 covers the epitaxial layer 302 and the oxide layers310, 313. According to the described structure, Schottky contacts areformed on the interface between the metal electrode 36 (or the adhesionlayer 34) and the epitaxial layer 302.

In a forward bias mode, the Schottky contacts between the metal layer 36and the epitaxial layer 302 have advantage of less power consumption.Furthermore, PN junctions consisting of the P-type doped regions 32 andthe lightly-doped N-type epitaxial layer 302 can hinder and pinch offthe current flow under the Schottky contacts as explained with referenceto FIG. 2. Based on the pinch-off effect, the reverse current leakage isthus suppressed. The embedded doped regions 32 do not narrow theSchottky contacts. Hence, it is not necessary to enlarge the size of thetrench Schottky rectifier device 3 to compensate for the reduced area ofthe Schottky contacts.

FIGS. 5A-5G illustrate a manufacturing method for forming the trenchSchottky rectifier device of FIG. 4 according to the present invention.As shown in FIG. 5A, a stack structure including a substrate 30, a maskoxide layer 310 and a first patterned photoresist layer 311 with atrench pattern is provided. The substrate 30 includes a heavily-dopedN-type silicon layer 301 and a lightly-doped N-type epitaxial layer 302.The mask oxide layer 310 on the substrate 30 is grown by thermaloxidation or deposition. The mask oxide layer 310 is then subjected toan etching step to partially remove the mask oxide layer 310 to expose aportion of the lightly-doped N-type epitaxial layer 302 according to thetrench pattern.

In FIG. 5B, the first patterned photoresist layer 311 is stripped off.Then, the epitaxial layer 302 is etched through openings of the maskoxide layer 310 to form the trenches 31 in the epitaxial layer 302. AnO2 based thermal procedure is performed to form thin sacrificial oxidelayers 312 on sidewalls and bottoms of the trenches 31. P-type dopantssuch as B ions or BF₂ are then implanted into the epitaxial layer 302through the bottoms of the trenches 31 to form the doped regions 32under the trenches 31. The doped regions 32 and the epitaxial layer 302will form PN junctions whose depletion regions can pinch off the leakagecurrent in the reverse bias mode.

In FIG. 5C, the thin sacrificial oxide layers 312 has been removed andgate oxide layers (insulating layers) 313 are formed to cover thesidewalls and the bottoms of the trenches 31. The removal of the thinsacrificial oxide layers 312 improves the smoothness of the surfaces ofthe trenches 31. The oxide layers 313 on the bottoms of the trenches 31are further etched off to expose the doped regions 32.

In FIG. 5D, a hard mask layer 33, for example a silicon nitride layer,is formed by a CVD procedure to cover the structure of FIG. 5C. A secondpatterned photoresist layer 314 for defining device area of the trenchSchottky rectifier device 3 is formed on the hard mask layer 33 and inthe trenches 31. Then, the uncovered hard mask layer 33 are removed by adry etching step, and the exposed mask layer 310 is also removed byanother dry etching step to expose the top surface of the epitaxiallayer 302 at the device area. FIG. 5E shows the obtained structure inwhich the second patterned photoresist layer 314 has been stripped off.

In FIG. 5F, the remaining hard mask layer 33 is removed, and an adhesionlayer 34 made of Ti or TiN is optionally formed on the surfaces of theoxide layers 310 and 313 by a sputtering procedure to enhance thebonding of the electrode 36 to the epitaxial layer 302 and the oxidelayers 310. The adhesion layer 34 may be subjected to a rapid thermalnitridation (RTN) process to enhance the bonding effect. Subsequently,the trenches 31 are filled with the metal structure 35, for example,made of W. In an embodiment, a metal layer such as a W layer is formedto cover the adhesion layer 34 by a CVD procedure, and then the metallayer is subjected to an etch-back procedure to remove a portion of themetal layer out of the trenches 31.

At last, the electrode 36 is formed on the obtained structure. In anembodiment, a metal sputtering procedure is performed on the structureof FIG. 5F to form the metal layer 36 overlying the adhesion layer 34and the metal structure 35. In an embodiment, the metal layer 36 is madeof Al or Al alloy. A rapid thermal processing (RTP) step can beperformed after the metal layer 36 is formed, so as to correct thedefects resulting from the metal sputtering procedure. Then, a thirdpatterned photoresist layer 316 is formed over the metal layer 36 (FIG.5G). Portions of the metal layer 36 and the adhesion layer 34 are etchedoff to form the electrode 36 according to the third patternedphotoresist layer 316. After the third patterned photoresist layer 316is stripped off, a sintering procedure may be performed to enhanceadhesion of the metal layer 36 (and the adhesion layer 34) to thesubstrate 30, the metal structure 35 and the oxide layer 310. It is tobe noted that the sintering procedure may be performed after each metalsputtering procedure. The resultant structure of the trench Schottkyrectifier device 3 has been described with reference to FIG. 4.Similarly, the trenches 31 and doped regions 32 in the inactive area ofthe trench Schottky rectifier device 3 of FIG. 4 are not essentialcomponents according to the present invention.

FIG. 6 is a cross-sectional view illustrating a further preferredembodiment of a trench Schottky rectifier device according to thepresent invention. Similar to the trench Schottky rectifier device 3 ofFIG. 4, the trench Schottky rectifier device 4 includes a substrate 40(including a heavily-doped N-type silicon layer 401 and a lightly-dopedN-type epitaxial layer 402), a plurality of trenches 41, doped regions42, metal structure 45, oxide layers 410, 413, an adhesion layer 44 andan electrode 46. The relevant components are not described verboselyagain. In addition, the trench Schottky rectifier device 4 includes aguard ring 405 in the edge area of the substrate 40 for improvinglatchup immunity of the device and preventing interference betweenadjacent devices. The guard ring 405 may be of P-type conductivity whenthe substrate 40 is a N-type substrate.

In a forward bias mode, the trench Schottky rectifier device 4 has lowforward voltage drop because of the Schottky contacts. Furthermore, in areverse bias mode, the reverse current leakage is suppressed because ofthe widened depletion regions of the PN junctions consisting the P-typedoped regions 42 and the N-Type epitaxial layer 402. It is to be notedthat the P-type doped regions 42 are located under the trenches 41 anddo not affect the area of the Schottky contacts.

FIGS. 7A-7H illustrate a manufacturing method for forming the trenchSchottky rectifier device of FIG. 6 according to the present invention.As shown in FIG. 7A, a stack structure including a substrate 40, a masklayer 408 and a first patterned photoresist layer 409 defining the guardring 405 is provided. The substrate 40 includes a heavily-doped N-typesilicon layer 401 and a lightly-doped N-type epitaxial layer 402. Themask layer 408 on the substrate 40 is grown by thermal oxidation ordeposition, and then subjected to an etching step to partially removethe mask layer 408 to expose a portion of the lightly-doped N-typeepitaxial layer 402.

In FIG. 7B, the first patterned photoresist layer 409 has been strippedoff. Then, an etching step is performed through the opening of the masklayer 408 to form a depression in the epitaxial layer 402. Subsequently,an ion implantation procedure is performed by using the remaining masklayer 408 as a mask to introduce dopants in to the edge area of theepitaxial layer 402, and thus the guard ring 405 is formed along thesurface of the epitaxial layer 402 in the edge area. The dopants mayinclude B ions or BF₂, and a thermal drive-in step or an annealing stepis optionally performed to allow better diffusion of the dopants oractivate the dopants. FIG. 7C shows the obtained structure in which themask layer 408 has been removed.

The subsequent steps are similar to those as described with reference toFIGS. 5A-5G. In FIG. 7D, the mask oxide layer 410 and a second patternedphotoresist layer 411 with a trench pattern is provided. The mask oxidelayer 410 is then subjected to an etching step to expose a portion ofthe lightly-doped N-type epitaxial layer 402 according to the trenchpattern.

In FIG. 7E, the second patterned photoresist layer 411 is removed. Then,the epitaxial layer 402 is etched through openings of the mask oxidelayer 410 to form the trenches 41 in the epitaxial layer 402. An O₂based thermal procedure is performed to form the thin sacrificial oxidelayer 412 on sidewalls and bottoms of the trenches 41. P-type dopantssuch as B ions or BF₂ are then implanted into the epitaxial layer 402through the bottoms of the trenches 41 to form the doped regions 42under the trenches 41. The doped regions 42 and the epitaxial layer 402will form PN junctions whose depletion regions can pinch off the leakagecurrent in the reverse bias mode.

In FIG. 7F, the thin sacrificial oxide layer 412 has been removed toimprove the smoothness of the surfaces of the trenches 41 and anotheroxide layers 413 are formed to cover the surfaces of the trenches 41.The oxide layers 413 on the bottoms of the trenches 41 are furtheretched off to expose the doped regions 42.

In FIG. 7G, a hard mask layer 43, for example a silicon nitride layer,is formed by a CVD procedure to cover the structure of FIG. 7F. A thirdpatterned photoresist layer 414 for defining device area of the trenchSchottky rectifier device 4 is formed on the hard mask layer 43 and inthe trenches 41. Then, the uncovered hard mask layer 43 and theunderlying mask oxide layer 410 are dry-etched off to expose the topsurface of the epitaxial layer 402 at the device area. FIG. 7H shows theobtained structure in which the third patterned photoresist layer 414has been stripped off.

In FIG. 7I, the remaining hard mask layer 43 is removed, and an adhesionlayer 44 made of Ti or TiN is optionally formed on the surfaces of theoxide layers 410 and 413 by a sputtering process to enhance the bondingof the electrode 46 to the epitaxial layer 402 and the oxide layers 410.The adhesion layer 44 may be subjected to a rapid thermal nitridation(RTN) process to enhance the bonding effect. Subsequently, the trenches41 are filled with metal structure 45, for example, formed by a CVDprocedure along with an etch-back procedure.

At last, the electrode 46 is formed on the resulting structure, as shownin FIG. 7J. In an embodiment, a metal sputtering procedure is performedon the structure of FIG. 7I to form the metal layer 46 overlying theadhesion layer 44 and the metal structure 45. In an embodiment, themetal layer 46 is made of Al or Al alloy. A rapid thermal processing(RTP) step can be performed to correct the defects resulting from themetal sputtering procedure. Then, a fourth patterned photoresist layer416 is formed over the metal layer 46 to define the electrode 46. Theresultant structure of the trench Schottky rectifier device 4 has beendescribed with reference to FIG. 6.

According to the present invention, the trench Schottky rectifier devicehas low forward voltage drop and rapid switching speed in the forwardbias mode. Furthermore, better than the conventional Schottky rectifierdevice, the Schottky rectifier device according to the present inventionhas low reverse leakage current in the reverse bias mode due to thepinch off effect as described above. The embedded doped regions 22, 32and 42 do not reduce the effective area of the Schottky contacts becausethey are located under the trenches 21, 31 and 41. Hence, the presentinvention overcome the problems of the prior arts and is highlycompetitive.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

What is claimed is:
 1. A method for fabricating a trench Schottkyrectifier device, comprising steps of: providing a substrate having afirst conductivity type; forming a guard ring having a secondconductivity type in an edge area of the substrate; forming a mask oxidelayer on the substrate and forming a plurality of openings in the maskoxide layer; forming a first plurality of trenches and a secondplurality of trenches in the substrate according the mask oxide layer;forming a plurality of doped regions having the second conductivity typein the substrate under the first plurality of trenches and the secondplurality of trenches; forming an insulating layer on sidewalls of thefirst plurality of trenches and the second plurality of trenches;keeping a first portion of the mask oxide layer to cover a first portionof the substrate and removing a second portion of the mask oxide layerto expose a second portion of the substrate; forming an adhesion layeron the first portion of the mask oxide layer, the second portion of thesubstrate, the insulating layer, bottoms of the first plurality oftrenches and the second plurality of trenches and in contact with theplurality of doped regions having the second conductivity type; fillingthe first plurality of trenches with a first plurality of conductivestructures and filling the second plurality of trenches with a secondplurality of conductive structures; and forming an electrode overlyingthe adhesion layer, the first plurality of conductive structures and thesecond plurality of conductive structures; wherein forming the guardring comprises removing a portion of the electrode and a portion of theadhesion layer in the edge area of the substrate.
 2. The methodaccording to claim 1 wherein before the step of forming the insulatinglayer on sidewalls of the first plurality of trenches and the secondplurality of trenches, the method further comprises steps of: forming asacrificial layer on the sidewalls of the first plurality of trenchesand the second plurality of trenches; and removing the sacrificial layerto smooth the sidewalls of the first plurality of trenches and thesecond plurality of trenches.
 3. The method according to claim 1 whereinthe substrate comprises a relatively heavily-doped N-type silicon layerand a relatively lightly-doped N-type epitaxial layer.
 4. The methodaccording to claim 1 wherein the step of forming the plurality of dopedregions further comprises a step of doping the substrate with P-typedopants through bottoms of the first plurality of trenches and thesecond plurality of trenches to form the doped regions.
 5. The methodaccording to claim 1 wherein the step of keeping the first portion ofthe mask oxide layer and removing the second portion of the mask oxidelayer further comprises steps of: forming a hard mask layer on the firstportion of the mask oxide layer, the second mask oxide layer, theinsulating layer and bottoms of the first plurality of trenches and thesecond plurality of trenches; removing a portion of the hard mask layerto expose the second portion of the mask oxide layer; removing theexposed second portion of the mask oxide layer; and removing the hardmask layer.
 6. The method according to claim 1 wherein the firstplurality of conductive structures and the second plurality ofconductive structures are metal structures.
 7. The method according toclaim 6 wherein the step of forming the first plurality of conductivestructures and the second plurality of conductive structures comprisessteps of: forming a metal layer covering the adhesion layer by achemical vapor deposition procedure; and performing an etch-backprocedure to remove a portion of the metal layer out of the firstplurality of trenches and the second plurality of trenches.
 8. Themethod according to claim 1 wherein the electrode is made of aluminum oraluminum alloy, and the adhesion layer is made of titanium or titaniumnitride.